The skin is our gateway to the physical world. Below its surface are oodles of nerve fibers relaying different types of messages to the brain. At the ends of the fingertips, for example, fat and fast Aβ nerves help you fish for keys at the bottom of a messy purse, or feel the difference between cotton and polyester. Nearby those big nerves are thinner and slower C-fiber nociceptors, which transmit pain, and others that relay itchiness.

What I didn’t know until this week is that there is yet another type of nerve, found only under hairy skin, that carries information about our social interactions. These nerves, known as C-tactile (CT) afferents, respond to slow, gentle stroking — the soft touch you’d give to a baby’s forehead or a lover’s arm. And some researchers believe that these fibers are crucial for the development of the social brain.

“A hand on the shoulder, a pat on the back — these things anchor and cement social relationships in a meaningful way,” says Francis McGlone, a cognitive neuroscientist at Liverpool John Moores University in the U.K.

In today’s issue of Neuron, McGlone and his colleagues published a commentary reviewing what’s known about these nerves, including some provocative studies suggesting they play a role in autism.

“This C-tactile system is not there to sense the physical world, it’s there to feel the physical world,” McGlone says. “It’s coding something very important, particularly during early development.”

CT nerves were first described in 1939. Swedish physiologist Yngve Zotterman found that in a cat’s leg, certain thin nerve fibers would fire electrical signals in response to slow stroking with the edge of a round wooden pin. “The complex response to stroking naturally raises the question whether the different groups of spikes are derived from groups of fibres with different sensory functions,” Zotterman wrote.

Subsequent studies confirmed that these nerves exist in cats (1957), as well as in monkeys (1977) and rats (1993). They weren’t reported in people until the late 1980s and ‘90s, thanks to a technique called microneurographypioneered by two Swedish scientists, Karl-Erik Hagbarth and Ake Vallbo. With this method (which Hagbarth and Vallbo first perfected on their own arms to prove its safety) a metal electrode tungsten microelectrode is poked through the skin of an awake person to record electrical signals from the nerves underneath.

Deciphering the code of these nerves is difficult and takes a lot of patience. “It’s like putting a microphone into a United Nations convention — there’s lots of different languages you’re going to be hearing,” McGlone says. “I think five people on this planet can record from C-tactile afferents.” These trained scientists can hear the language (that is, a certain pattern of electrical waveforms) of the CT afferents only when the skin is gently stroked.

McGlone’s lab has done a series of fascinating studies on CT afferents. His team uses a robotic stimulator to deliver gentle brush strokes in a steady, consistent way. Here’s a quick video of how it works:

The person in the video is rating how pleasant (or unpleasant) the touch feels on different parts of his body. In 2009, McGlone’s team published a study in Nature Neuroscience in which this robotic brush stroked volunteers at different velocities. Turns out that the velocities that volunteers rated as most pleasant are the same ones that activate CT nerves. “They matched up perfectly,” McGlone says.

OK, so there are nerves that selectively respond to a soft touch. The real question is, why? What are they for?

“We’re still asking that question,” McGlone says. “What I hope I’ve done in this new paper is put a few more pieces of the jigsaw puzzle in place.”

Several puzzle pieces come from brain imaging studies. In 2012, for example, McGlone and collaborators in Montreal scanned volunteers’ brains while slowly stroking two skin areas: a hairy patch of the forearm, which holds CT fibers, and the hairless palm, which does not have CT fibers. Stroking CT fibers triggered activity in the posterior insular cortex and mid-anterior orbitofrontal cortex, which are both part of the brain’s limbic system, deep circuits that process emotion. Stroking the palm, in contrast, activated the somatosensory cortex, the outer layers of brain that process our physical sense of touch.

Stroking CT fibers also activated a brain region called the angular gyrus, which is involved in our internal representation of our body. (In studies of epileptic patients, stimulating this region leads to dramatic out-of-body experiences.) This result is intriguing, McGlone says, because it suggests that CT afferents are involved not only in our awareness of others, but in our physical sense of self.

The same brain regions activated by CT afferents — the insular cortex, orbitofrontal cortex, and angular gyrus — have also been implicated in autism and related disorders. Could autism be the result of an impaired touch system?

Pelphrey is most interested in one of those brain regions, the superior temporal sulcus, or STS. This area is sensitive not only to social touch, but to socially meaningful sights and sounds. “We’re working on smells now as well,” Pelphrey says. His earlier work has shown that children with autism have abnormally low activity in the STS.

Pelphrey has also scanned the brains of children with autism while they felt slow or fast arm-stroking. “We wanted to know if the brain response to social versus non-social touch is present in autism or not, and to what degree it’s disrupted,” he says. “We found something,” he says, but wants to keep the results under wraps because the study is currently under review.

There are other reasons to suspect that CT afferents may be involved in autism, Pelphrey says. Many individuals with autism, such as autism advocate Temple Grandin, have sensory sensitivities. Pelphrey notes that some of the earliest descriptions of the disorder mention that babies with autism don’t react to being picked up in way that most babies do. “Touch is the first sensory system to develop,” Pelphrey says. “The brain response to C-tactile afferents should be present well before birth.” So if the system is disrupted in autism, it could become a very early biomarker of the disorder.

The question of why these afferents exist is still open. They could be vestigial, useless leftovers of our evolutionary past, the skin’s appendix. But McGlone doesn’t think so. He believes that affective touch is crucial for our brain development, and worries about what will happen as we transfer more and more of our social lives online.

“We live in a touch-deprived world,” he says. “You can see sort of an Armageddon scenario, where the affective touch system may well become vestigial. And what would the consequences be for the social brain?”

*

The text has been slightly modified: The electrode used in microneurography is made of tungsten, not metal.

Related

30 thoughts on “The Roots of Autism Are in the…Skin?”

Many autistic children arch when held as babies, as though touch is painful. Grandin used deep pressure, not light social pressure, to calm her nerves. She said following using her “squeeze machine” she could feel emotions of tenderness and love. Parents have long used deep pressure to calm their children because of it. Look at weighted blankets that allow some children to fall asleep, and calm frazzled nerves, for the first time in their lives. I think we need to look not at what “normal” is, and try to make autistics mimic “normal”————-but we need to look at what austic children _need_, and what their bodies reaction to touch is telling about their skin/nerve endings. A touch deprived world will not make people autistic…but touch that feels like electric jolts will make autistic people sensorily defensive.

Science so desperately needs to listen to what thousands of autistics are trying to tell them…rather than drumming ups scary scenarios of things they don’t understand. The most ignorant person is the one who thinks he can read the minds and hearts of others, without asking the others. Armageddon?? For the love of God…

I apologize…bad week for autistics. There is a saying among enlightened mothers, Love not Fear. So much science regarding autism is worded so unkindly towards them. I read the end, and couldn’t even tell you what the rest of the article said. Put yourself in their skin for one day. There is an obsession with social deficits, but in many ways it is the least of it. A parent is in a much different position than any curious scientist will ever be.

Is the author implying the old “parental neglect causes autism” refrain? Or that autistism keeps infants from receiving the benefits of touch and therefore being able to develop socially? Why would the STS be under-active if what most autistic people experience is over-stimulation of those senses mentioned?

No, I wasn’t implying that parental neglect causes autism. I apologize if it came across that way. The researchers who believe that the touch system is impaired in autism speculate that it could begin prenatally, which would be no “fault” of the parents.

I’m a poor spokesperson for parents. I was raised by a bartender father and I tend to be a little cynical, but I’ll try to explain kindly. I am a teacher…and my son ended up with learning differences. I met a mother, Dr. Glennis Sternberg, who started an award winning school for kids with LD and all kinds of labels. She had been a special educator in a public school and HAD NO IDEA…She had sat on both sides of an IEP meeting. As a professional she had been cool, calm, and collected—but when it concerned her child, she sat on the other side of the IEP meeting and sobbed at the first meeting.

I’m sorry you don’t agree with my choices of language as far as “person with autism” versus “autistic”. People in the autism advocacy world don’t seem to agree on this usage question, either, and it’s certainly something that we should all be having an open discussion about.

Interesting article, but the title seems to suggest that a lack of touch -causes- autism rather than being a marker for it. It’s really too early to call that one. As an inhabitant of an autistic brain (I have Asperger’s), there are a lot of differences in the ways autistic brains are wired.

I personally agree with an article which said that the brain’s built-in inhibitors don’t function as well in those with autism. It certainly makes sense to me: I had certain OCD tendencies because of nagging thoughts that wouldn’t go away. I was super sensitive to certain stimuli. It also explains my thought processes: I always had to consider every option thoroughly, because my mind couldn’t discard ideas. The neurons just kept firing.

So that really makes sense to me – neurons/neuronal paths keep firing in autistic brains due to an underfunctioning inhibitory system. But as for what causes that? I guess this touch thing is a theory, but somehow I think it’s more than that.

Virginia…parents and OT’s have used “therapy”, using a soft brush to gently tone down the child’s hypersensitivity to touch for over 50 years. I’m pretty sure I learned it in college 30 years ago. Jean Ayres, OT, recommended it in 1964. I used it in my classroom in 2007. I don’t know if you can imagine what it feels like to see all of this stuff come up like it is some new, brilliant idea when it seems there is nothing new under the sun. Parents, in the past, did not have access to research as it “goes live” so to speak. It is so hard for me to shut up, but I am so frustrated. It’s like all this stuff is being recycled. Like we haven’t been trying our hearts out, and somebody comes up with an idea, and thinks they have the key…when it’s already been done.

I have to get off the internet. This isn’t good, to be so frustrated. I feel like I am picking on you.

This article is so interesting and enlightening to me. I have always felt flashing lights and sound on my skin. Almost like the signals get crossed in my brain and my skin has eyes and ears. It may not be exactly the same but it does explain some things for me. Wish I could find out more. Prayers for those dealing with autism and for you to all find ways to communicate and share your love.

Sounds like you and your colleagues have found significant information and are sharing that info. I found your article very interesting. I think there are lots of critics out there assailing you. I did not get the sense that you were inferring that parents were, in any way, the cause of a child’s autism. If parents and teachers used touch therapies in the past because they would try anything to effect change, that makes sense. It just seems that your critics don’t fully understand your work. You were kind to respond so nicely to their criticisms.

I sometimes care for two teens with autism. Their mom said they were kids with autism, not autistic kids. The autism didn’t define who they were.

The article isn’t saying that a lack of touch causes autism, or that autism can be “treated” with soft touch. It is pointing out a connection between a difference in CT nerve response and autistic traits and suggesting that autism as a whole may be rooted in a difference in those CT nerves. It doesn’t say anything about the reason CT nerves could be different/impaired. That said, the last two paragraphs make a jump for dramatic effect that seems to throw people off the original point.

Julia, the author clearly asks, “Could autism be the result of an impaired touch system?”. The title of the article implies that the root of autism is in the skin.
So, you’re right… the article does not say verbatim that a lack of touch causes autism. However, continuously drawing parallels without proper evidence to support the theory can be a bit misleading for some people out there looking for answers around autism. Language around these kinds of topics is crucial. That being said, I would hope that everyone would read this article and understand that this is work in progress and that more research is needed.

Virginia, I would always air on the side of caution of the person of whom you are speaking about. Go straight to the source and ask. If autistic people are choosing to be called that, but advocates are pushing a different choice word, I would side with the autistic person. You can then kindly inform the advocate that they are no longer needed! The middle man has been cut out; the autistic has spoken, signed, gestured, used pecs, flapped their hands, nodded, you get the point.

Thanks for this perspective. I know of people with autism who prefer the “people with autism” term over “autistic” as well. Some people don’t believe that their entire identity can or should be reduced to a diagnosis. I don’t call people with anxiety “the anxious”, nor people with OCD “obsessives”. It’s a semantic choice, and an important semantic choice, and I understand that people have differing opinions on it.

I really admire how non-defensively you react to comments that are coming from someplace other than reading your article. The information it contained was new to me, and very interesting. It’s useful that researchers are studying therapies that have “already been done” to understand why they might be effective–thanks for writing.

Very interesting research. I’m an Aspie, and I’ve always been hypersensitive to touch. It took me many years to learn not to flinch when someone touched me unexpectedly, such as putting their hand on my shoulder or arm. I get fewer mosquito bites because I can feel as soon as a mosquito touches a single hair and swat it before it can bite. I won’t even get into cutting tags off clothes, not being able to wear wool, etc.

research science tries to get to the root of the matter. your rant about how this was already known shows how little you know about the true purpose science (drilling down to get to the least-wrong theories). scientists want to know EXACTLY (or as close to knowing) what is happening while minimizing confounding variables that could lead others (non-rigorous non-scientists) astray into confirmation bias-land.

you should be relieved and emboldened that scientists are confirming your “knowledge” of OT therapeutic intervention rather than saying they are slow to the party. the equipment necessary to even prove these – “tried & true” interventions are valid – has only become readily useful in recent history. so, applaud their work and hope that the research gains even more knowledge than what was instinctively brought forth 50 years ago.

Brolan, I don’t know why, but I am not thankful. It wasn’t my knowledge, but Jean Ayres, and that of my education professors. I feel like I’ve seen the wizard of Oz spinning furiously, trying to keep up the notion that it is only just a man behind the curtain.

Science refuses to see the elephant, because each has a limited scope of understanding. They attempt to fit an idea of autism into the paradigms they already hold. This, often times, is in accord with the work they do in their labs. With 1.5 billion dollars given out to autism research, we still have not one definitive clue, but we have a lot of wealth incurred. It would be amusing, except that it doesn’t help the kids. In fact, looking at where the science is going, it often leads to abusive practices, no matter how much autistic individuals try to educate scientists of the PTSD they suffered from helpful “therapy” as children…

I know I am ignorant, but the above work was done 20 years ago. It speaks to me. Sfari asked once what indicator I wish science would pay attention to. I said toe walking. The motoric anomalies of autism are ignored. The cerebellum is implicated, or even the brain stem. It was either thalidomide or valproic acid damage induced in days 20-24 of fetal development (freaking selective, eh?), that coincides with autism in the child…these coincide with cerebellum development in the fetus. The brain begins with the brainstem and increasing complexity occurs, ending with the frontal lobes, from my faulty memory. Early teratogenisis, early maladaptive genetic anomalies…even the skin anomalies, apparent because the skin develops in conjunction with the nervous system…from what I”ve been told, are apparent in the indicators of Tuberous Sclerosis, and Neurofibromatosis (ash leaf spots, cafe au’ lait spots, hemangionomas, something that looks like the skin of an orange, don’t remember the name)….all of these are indicators of early genesis of autistic tendencies, whether it is iatrogenic or genetic in origin.

“And related disorders”…do you mean other personality disorders? Because Narcissistic personality disorder has been involved with recent experiments involving these brain regions with some facinating results.
Autism and psychopathy may be on the same spectrum (opposite ends) according to neurobiologists like Simon Bahron-Cohn.
This area of study is so fascinating to me because of its bigger implications- the mechanics of consciousness?
Comparing people operating normally (developed self) vs those who lack an internal developed self (personality disordered people) may reveal one of life’s biggest mysteries.. the physiology of self.

and mentioned a report that says “Four out of five people with psychiatric disorders live in developing countries, where they have few opportunities for treatment.” I left a comment on that post asking you what report is sited on your article.

As an early childhood specialist I find this article interesting, and yes some of this info is not new…my mother was a PT for birth-3 for 30 years & I remember learning about gentle brushing techniques as a child (20+ years ago). I must add here that I too, DID NOT GET TJE IMPRESSION FROM ANYTHING IN THIS ARTICLE THAT IMPLIED “PARENT NEGLECT”, NOR DO I FEEL THEY PASSED ANY JUDGEMENT TOWARD PARENTS.
And also, the language discussion, it’s called PEOPLE FIRST LANGUAGE. Its very important to focus all efforts as the writers here did & not use phrases like “Autistic Kids” or especially “autistics” (yikes!)! Because FIRST, they’re children…end of story. Anything else certainly makes up unique traits & characteristics but above all it’s a person, a human, a child, then let’s add the rest!

To me this article demonstrates what has been happening for many years in relation to science and the Autistic Spectrum Disorder. That all the anecdotal evidence provided by parents, carers and those kids with ASD previously ignored or written off because it was anecdotal and not supported by statistical surveys and blind-studies etc is now being shown to have validity. The saying “if you have met one autistic child, you have met one autistic child.” still applies today but science should not use the individuality of the child’s behaviours as an excuse to not accept it as being valid or to not investigate it. Get away from the idea too that autism is a psychological, mental, or psychiatric disorder. It is a neurological condition and should always be regarded and referred to as such. These kids and their parents have to deal with enough misunderstanding and social stigma as it is without adding to it by those misnomers.

Virginia,
Thank you for (another) well-written, responsible piece of writing. Something of a rarity.
As regards the ‘roots of autism’, studies such as those referenced here are encouraging in that they examine the *autistic experience* rather than trying to define the nature of *autism*. That is a crucial difference, and one that ties in to the debate about ‘autistic’ vs. ‘person with autism’. Autism cannot exist without the autistic and can, at best, be regarded as a set of symptoms of something deeper. When an autistic discusses the characteristics of their difference, almost all (I have seen 95% referenced and am still trying to pin down the source) note sensory sensitivities or insensitivities as prominent characteristics. This does include touch (deep pressure, stroking, tickling, textures, the horribleness of clothes labels, etc), but also excellent night vision, painful bright lights, hyper-sensitive hearing, discomfort at high or low pitch sounds, hyper-sensitive smell, aversion to particular smells or flavours – the list goes on. This list also includes synaesthesia, which has been shown to be far more common among autistics than others and is, I suspect, far more common even than records suggest. These are *experiences* of *autistics* – they help shape how an autistic experiences the world. They can be defined as extreme sensory experiences – hyper- or hypo-sensitivity. That is what characterises them and defines their relationship.
Now consider the characteristics which tend to get prominence in the definition of autism – poor social skills, poor fine or gross motor skills, poor language ability, poor intellectual ability, meltdowns and shutdowns… These are all secondary symptoms of something else. They are about how others perceive difference in an autistic, and notably they are all quite negative, focusing on deficits of various kinds.
When autistics discuss these types of ‘deficit’ they of course express frustration at the limitations they create, but time and again, as discussion proceeds, they are quickly put into context. That context is almost always described in terms of sensory overload or mixing – unable to process conversation due to a constant clatter of background noise, unable to function optimally in an office or classroom due to the hum and glare of flourescent lighting, distracted by nauseating effects of subtle smells. Those symptoms are autism. The causes are again and again reported to be mainly a result of the autistic experience of this world.
There is surely more to the picture than this, but the nervous system from nerve tip right through to the brain, and the working of the brain itself, does seem to be central to the picture.
That’s why I choose to describe myself as autistic, not as aperson with autism. It *is* part of me, my personality and my experience, not an add-on. Others have their own reasons for choosing one wayor the other, but autistics themselves are increasingly opting for ‘autistic’, with analogies drawn to ‘blind’, ‘redhead’, ‘German’, etc – part of who you are but by no means the whole story.
Last comment – the reference by McGlone to an ‘armageddon’ is unfortunate and unscientific speculation. Placed in the context of a discussion relating to ‘the roots of autism’ it does nothing but reinforce negativities that do damage to autistic individuals, and perpetuates a strongly negative word-set that helps focus research mainly on ‘deficits’ and ‘disorders’… and on causes, cures and preventions. That in turn affects media representations, which shapes public perceptions and the cycle continues. I’d like to commend you for avoiding most of the easy assumptions that tend to beset discussions of the autistic experience. Big thumbs up!

As an elementary special education teacher, I see similar sensory issues in students with ADD/ADHD. I’m very interested in the similarities between ADD/ADHD and ASD. I am sorry so many readers have chosen to focus on whether or not you use the term ‘autistics’ or ‘people with autism’ or any other way of classifying individuals who are ‘on the spectrum.’ I also thought it was clear that you were explaining the possibility that some interference with the development of the nervous system may be occurring in prenatal development, that in turn, effects social development. Thank you for the information. I hope this research leads to practical uses for prevention and therapy in the near future.

@ Virginia Hughes: True, the Autism Community is 50/50 on person-first language vs identity-first language, but the vast majority of the #ActuallyAutistic Community prefers identity-first language to be used. That’s why I use it almost exclusively, making exceptions only for individual Autistic people who state that they prefer I use alternative terminology about them.

About Virginia

I'm a freelance journalist who writes about neuroscience, genetics, behavior, and medicine for the likes of Nature, Popular Science, and Slate. Before coming to Phenomena, I contributed to the delightfully quirky science blog The Last Word on Nothing. I live in Brooklyn, New York, land of artisanal basketball stadiums and rich dog walkers, with my husband.

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Virginia Elsewhere

Uprooted, a longform narrative published in MATTER, investigates the rapidly growing industry of genetic genealogy. Deep down, everybody wants to know who they are and where they came from. But what happens if you discover that everything you thought was true was, in fact, a lie?

Re-Awakenings, a story about a strange sleeping sickness published on The Last Word on Nothing, was deemed best post of 2012 by Science Seeker.